In unitate fidei
The apostolic letter Pope Leo XIV issued on the 1,700th anniversary of the Council of Nicaea, days before his journey to Türkiye, on the creed of Nicaea and its value as common ground among Christians.
The letter has twelve numbered sections and ends with a prayer to the Holy Spirit. Sections 3 to 8 retell the council and its aftermath as the Catholic Church reads them: the dispute over Arius, the summons by the emperor Constantine, the word homoousios, and the completion of the creed at Constantinople in 381. Sections 9 to 11 ask what the creed demands today, and section 12 treats its ecumenical value.
Two points matter for the wiki’s long thread on East and West. Section 8 quotes the creed’s article on the Holy Spirit in the form “who proceeds from the Father”, and footnote 10 states that the words “and the Son” are not in the text of 381, that Pope Benedict VIII inserted them into the Latin creed in 1014, and that they are a subject of Orthodox–Catholic dialogue. The letter is a present-day papal document and is not evidence for the fourth century. See the Churches Mark 1,700 Years since Nicaea.
Cited in
- 28 November 2025, firm date